This invention relates to medical instruments. In particular, it relates to a laryngoscope for use in diagnosis, biopsy, the introduction of instruments or tubes into the trachea, and other like operations.
In the past, laryngoscopy was performed using laryngoscopes with either curved or straight blades. The choice of blade shape depended on which of two methods the physician preferred. The two methods are, however, only slightly different. In either method, the purpose of the blade is to push the tongue and other soft structures of the upper anterior neck forward. This displacement would permit a straight line of vision from the patient's upper teeth to the larynx. However, in some cases the head of the patient could not be adequately extended; this would prohibit the physician from seeing the larynx. Additionally, with either the straight or curved blade, intensive pressure was required to move the anatomic structures. In exerting the required pressure, the physician would sometimes have to pry against the patient's upper teeth. This, of course, introduced the possibility of damage to the patient's teeth.
Once a line-of-sight was obtained between the patient's upper teeth and the larynx, the physician was still faced with the problem of getting enough light to illuminate the larynx in order to see the larynx. Laryngoscopes which had illuminating provisions were of generally two types. The first type incorporated a light bulb at the tip of the laryngoscope. Typical of these is the patent to Vellacotie U.S. Pat. No. 3,595,222. This light bulb would give off considerable heat. As such, there was the possibility of burning the larynx of the patient. Also, in certain operations, blood might be present around the tip of the laryngoscope where the light bulb was housed. In this case, the heat from the light bulb tended to encrust the blood around the light bulb. This severely reduced the illumination of the larynx.
The second type of illuminating laryngoscope incorporated a light ducting means to guide the light from the light bulb to the tip of the blade. The light bulb was typically mounted within the handle of the laryngoscope. With the light bulb mounted in the handle the heat problem was eliminated. However, this posed the problem of getting enough light from the light bulb to the tip of the blade in order to illuminate the larynx. Some laryngoscopes incorporated lucite or plexiglass light guides. Typical of these is the patent to Reich, U.S. Pat. No. 3,638,644. Lucite and plexiglass light guides emit light around the entire circumference of the guide. Additionally "lucite" and "plexiglass" have a high coefficient of attenuation to light. This reduces the amount of light available at the tip of the laryngoscope. Also, acrylic resins such as "lucite" are lacking in the required mechanical properties. Lucite is a very brittle material and tends to crack with age. A crack in lucite is a glassy fracture. This fracture can reflect as much light back to the source as passes through the fracture. An additional problem with lucite is that is cannot be sterilized by boiling water. In order to sterilize and at the same time prevent the lucite from softening, chemicals such as ethylene oxide must be used.